JET ENGINES DESIGN Design of jet engines
The force system of the engine is used to transfer all forces occurring during operation of the engine and transfer the final thrust on a airframe It consists of: - force elements of air intake, - Compressor casing, - Combustion chamber casing - Turbine casing, - Separate the bearing housing , - Force elements of exhaust system .
* Design of jet engines
Force system with internal coupling * Design of jet engines
Force system with external coupling * Design of jet engines
Force system with double open coupling * Design of jet engines
Force system with internal coupling R-11 F-300 engine
* Design of jet engines
Bearings:
The main engine bearings support the turbine and compressor assemblies. In the simplest case (a single spool engine), these usually consist of a roller bearing at the front of the compressor and another in front of the turbine assembly, with a ball bearing behind the compressor to take the axial thrust on the main shaft. “Squeeze film” main bearings have been introduced to reduce transfer of rotor vibration to the aircraft. In this type of bearing pressure oil is fed to a small annular space between the bearing outer track and the housing. Design of jet engines
Bearings:
* Design of jet engines
Bearings: “Squeeze film” on main bearings.
Squeeze Film Bearing. Figure 10.1. Design of jet engines
Bearings:
Various bearings type for jet engine Design of jet engines Typical bearings location Uložení rotujících částí:
* Design of jet engines
Sealing
Sump Vent Bearing chambers are usually sealed using air. The internal cooling air within the engine provides the air. Typical seals used are labyrinth, screw back and carbon types. All of these seals need a differential pressure between inside and outside the bearing housing. Where pressure is available it is used, if the differential is too low, it can be boosted by suction from a scavenge pump. Carbon seals require the oil to be in contact with them to provide cooling for the seal. Cavity Drain Oil Drain Honeycomb Seal Design of jet engines
Sealing
M - 701 engine Design of jet engines
The labyrinth seal may be used in conjunction with an abradable coating on the stationary member :
* Design of jet engines
Accessory Drive Gearboxes : – Gearboxes provide the power for aircraft hydraulic, pneumatic and electrical systems in addition to providing various pumps and control systems for efficient engine operation. The high level of dependence upon these units requires an extremely reliable drive system. – The power for the gearbox is typically taken from a rotating engine shaft usually the HP shaft, via an internal gearbox, to an external gearbox that provides a mount for the accessories and distributes the appropriate geared drive to each accessory. A starter may also be fitted to provide an input torque to the engine. An accessory drive system on a high by-pass engine takes between 400 and 500 horsepower from the engine.
* Design of jet engines
Skříně pomocných pohonů: Design of jet engines
Accessory Drive Gearbox:
Fuel Pump Permanent Magnet Alternator Oil Level / Temperature Sensor
Oil Reservoir
Start Control Valve
Starter Intregrated Drive Generator Design of jet engines
External Gearbox
* Design of jet engines
Internal Gearbox
Types of Internal Gearbox Figure 8.9. * Design of jet engines
Internal Gearbox
* Design of jet engines
Accessory Gearbox - Geartrain
* Design of jet engines
On multi-shaft engines, the choice of which compressor shaft is used to drive the internal gearbox is primarily dependent upon the ease of engine starting. This is achieved by rotating the compressor shaft, usually via an input torque from the external gearbox. In practice the high pressure system is invariably rotated in order to generate an airflow through the engine and the high pressure compressor shaft is therefore coupled to the internal gearbox.
* Design of jet engines
Example of integral Gearboxes housing KONSTRUKCE LOPATKOVÝCH MOTORŮ
Example of separable Gearboxes housing * Fuel system
Fuel system:
– The thrust of a turbo jet is controlled by varying the amount of fuel that is burnt in the combustion system and in order to operate the safe temperature limits, the amount of fuel that is burnt must be governed by the amount of air that is available at the time. – The air supply is dependent upon the RPM of the compressor and the density of the air at its inlet, so under a constant set of atmospheric conditions, the RPM of the compressor is an indication of the engine thrust. – The pilot has control of the fuel flow to the combustion system and is able to select any compressor RPM, between ground idling and the maximum permissible which is required for take off conditions, by the operation of a cockpit lever. Fuel system
Fuel system –main parts:
• Aircraft Mounted Components – Fuel Tanks. Stores sufficient fuel for the aircraft’s designed flight duration – Booster Pump. Ensures a constant supply of fuel at low pressure to the inlet of the engine driven HP Fuel Pump. – Low Pressure Cock. Isolates the engine fuel system from the aircraft fuel system in the event of engine fire or for maintenance. Fuel system
Fuel system –main parts:
• The Engine LP fuel system – LP Fuel Pump – Fuel/air heat exchanger . – LP Fuel Filter . • The Engine HP Fuel System – HP Fuel Pump + Fuel Control Unit – Dump Valve – Burners Throttle and HP cock – Fuel Flowmeter. – Pressurising and Fuel system
Fuel distributed around center of gravity Fuel system
LP HP Fuel system
The Engine LP fuel system - components Fuel system
Fuel pumps
Fuel system
The Engine LP fuel system – components Fuel system
Fuel system - filters: -Common practice to filter fuel -Incorporate a by-pass -Relief valve -Protect the system components from contamination
* Fuel system
BA flight 38 accident
Fuel heater Fuel system
Fuel system – Fuel pumps:
– The type of fuel pump used may vary from one engine type to another and their common purpose is to supply the correct amount of fuel to the burners at a sufficient rate of flow to ensure operation over the whole range of engine operation. – The pump is driven by the engine via a suitable gear train. – There are two basic types of fuel pump, the plunger- type pump and the constant delivery gear-type pump;
* Fuel system
Fuel system - pumps: Regulation servo Plunger type The fuel pump consists of a rotor assembly fitted with several plungers, the ends of which project from their bores and bear on to a non-rotating camplate or swashplate. Due to the inclination of the camplate, movement of the rotor imparts a reciprocating motion to the plungers, thus producing a pumping action. Large engines The stroke of the plungers is require aprox. determined by the angle of 55kW for drive inclination of the camplate. fuel pump Fuel system
Fuel system - pumps: MAX
‘STEADY-STATE’ FUEL DEMAND GAL/HR FUEL LTR/SEC FLOW
‘STEADY-STATE’ CRUISE CAMPLATE CRUISE ANGLE FUEL FLOW
IDLE
CRUISE IDLEENGINE RPM RPM MAX Fuel system
Fuel system - pumps: Gear type The gear-type fuel pump (see figure11.3.) is driven from the engine and its output is directly proportional to its speed. The fuel flow to the spray nozzles is controlled by re- circulating excess fuel delivery back to inlet. A spill valve, sensitive to the pressure drop across the controlling units in the system, opens and closes as necessary to increase or decrease the spill.
Gear Type Fuel Pump System. Figure 11.3. Fuel system
Fuel system - pumps: MAX
FUEL FLOW
GAL/HR SPILL LTR/SEC FLOW
COMBUSTION IDLE FLOW
IDLEENGINE RPM MAX GEAR TYPE PUMP Fuel system Fuel Control Unit :
The fuel control unit FCU meters the amount of fuel required by engine based on a conditions at a given moment: a) Required power b) The pressure of the ambient air c) Ambient air temperature d) The speed of the high / low pressure compressor e) The pressure delivery by the compressor
.
Fuel system Fuel Control Unit :
The controlling principle of a flow control system is that a constant throttle pressure drop is maintained irrespective of throttle area (position) for a given height and speed.
Fuel flow = Orifice area x Pressure drop
Principle of Fuel Metering Valve. Figure 11.4. Fuel system Fuel Control Unit : In hydro-mechanically operated flow control units (FCUs), the method of control is to use servo fuel as a hydraulic fluid to vary fuel flow (eg. by varying pump swash-plate angle). The pressure of the servo fuel is varied by controlling the rate of flow out of an orifice at the end of the servo line; the higher the outflow, the lower will be servo pressure and vice versa.
Kinetic Valve Figure 11.8. Half Ball Valve System. Figure 11.7. Fuel system Fuel Control Unit : The Simple Flow Control Unit comprises a half-ball valve acting on servo fuel bleed, whose position is determined by the action of an evacuated capsule
(immersed in P1 air) and a piston subjected to the same pressure drop as the throttle valve. Fuel from the pump passes at pressure P pump through the throttle, where it experiences a pressure Simple Flow Control. drop to burner pressure P burner. Figure 11.9. Fuel system Fuel Control Unit : The Proportional Flow Control Unit was designed for use on large engines with a wide range of fuel flow. The problem of
accurate control over this wide range was overcome by operating the controlling elements on a proportion of the main flow. The proportion varies over the flow range, so that at low flows a high proportion is used for control and at high flows, a smaller proportion. Fuel passes into the controlling (or secondary) line through a fixed secondary orifice and flows out through another orifice to the LP side of the pump. Secondary flow is controlled via the proportioning valve and sensing valve, which Proportional Flow Control. Figure 11.10. maintains an equal pressure drop across the throttle valve and secondary orifice. Servo pressure is controlled by a half-ball valve
operated by P1 and by secondary pressure. Fuel system Fuel Control Unit :
The function of the Acceleration Control Unit (ACU) is to provide surge-free acceleration during rapid throttle openings.
Acceleration Control Using Compressor Discharge Pressure. Figure 11.11. Fuel system Fuel Control Unit :
On engine are installed some protection devices that will override any excessive demands made on the engine by the pilot or by the control units. Typicall protection devices are: Top Temperature Limiter Power Limiter Overspeed Governor Fuel system
Fuel Control Unit : Metric valve
Engine deceleration pressure Bypass valve
drain
Starting fuel
acceleration pressure From fuel tank
generator turbines RMP regulator
Free turbines RMP regulator Fuel system Fuel Control Unit : Fuel system Fuel Control Unit :
Hydro - mechanical FCU of TV2 engine Fuel system Fuel Control Unit :
Examples of fuel metric units for small jet engines Fuel system
Burners:
– The usual method of atomising the fuel is to pass it through a swirl chamber where tangentially disposed holes or slots impart swirl to the fuel by converging its pressure energy to kinetic energy. In this state, the fuel passes through the discharge orifice where the swirl motion is removed as the fuel atomises to form a cone-shaped spray. – The shape of the spray is an important indication of the degree of atomisation; thus, the rate of swirl and therefore the pressure of the fuel at the burner are important factors in good atomisation.
* Fuel system
Burners type:
– Simplex
* Fuel system
Burners type:
– Simplex
Ideal pattern
* Fuel system
correct wrong The Simplex burner was first used on early jet engines. It consists of a chamber, which induces a swirl into the fuel and a fixed area atomising orifice. This burner gave good atomisation at the higher fuel flows, that is at the higher burner pressures, but was very unsatisfactory at the low pressures required at low engine speeds and especially at high altitudes.. Fuel system
A Duple or Duplex Burner require a primary and a main fuel manifold and have two independent orifices, one much smaller than the other. The smaller orifice handles the lower flows and the larger orifice deals with the higher flows as the burner pressure increases. A pressurising valve may be employed with this type of burner to apportion the fuel to the manifolds. As the fuel flow and pressure increase, the pressurising valve moves to progressively admit fuel to the main manifold and the main orifices. This gives combined flow down both manifolds. In this way, the Duplex and the Duple burner are able to give effective atomisation over a wider flow range than the Simplex burner for the same maximum burner pressure.
Duplex burner type Fuel system
The spray nozzle carried a proportion of the primary combustion air with the injected fuel. By aerating the spray, the local fuel-rich concentrations produced by other types of burner are avoided, thus giving a reduction in both carbon formation and exhaust smoke. An additional advantage of the spray nozzle is that the low pressures required for A Spray Nozzle. Figure 11.21. atomisation of the fuel permits the use of the comparatively lighter gear-type pump Fuel system
The spray nozzle Fuel system Fuel system Fuel system
Fuel nozzle test bed device Oil system
Oil system: • The gas turbine engine is designed to function over a wider environment and under different operating conditions from its piston engine equivalent and therefore special lubricants have been developed to cope with the following main problems: – High rpm compared with piston engines – Cold starting in winter can mean initial bearing temperatures of -54C which rapidly increases after starting to 232C. Therefore a good viscosity index and adequate cooling are required. – There are fewer bearings and gear trains – Oil does not lubricate any parts directly heated by combustion and therefore oil consumption is low – There are no reciprocating loads – Bearings are generally of the rolling contact type and therefore only low oil pressures are needed (40 psi is normal). * Oil system
Oil system: • There are basically two types of lubrication system at present in use in gas turbine engines:- – Recirculatory. In this system, oil is distributed and returned to the oil tank by pumps. There are two types of recirculatory system:- • Pressure relief valve system. • Full flow system. – Expendable.
* Oil system
Expendable system: nádržTank SVPump VV
doTo atmosphereatmosféry LLM
An expendable system is generally used on small engines running for periods of short duration. The advantage of this system is that it is simple, cheap and offers an appreciable saving in weight as it requires no oil cooler, scavenge pumps or filters. Oil can be fed to the bearing either by a pump or tank pressurisation. After lubrication the oil can either be vented overboard through dump pipes or leaked from the centre bearing to the rear bearing after which it is flung onto the turbine and burnt. * Oil system
Recirculatory system:
Oil pressure Filters and tank pumps heat exchanger
scavenge pumps
* Oil system
Main components of oil system
The oil pumps - fitted in a recirculatory system are normally gear-type or Gerotor type pumps. The pumps are usually mounted in a pack containing one pressure pump and several scavenge pumps. They are driven by a common shaft through the engine gear train. Oil system
Main components of oil system
Typical gear type oil pumps with numerous rotors Oil system
Oil coolers - All engines transfer heat to the oil by friction, churning and windage within a bearing chamber or gearbox. It is therefore common practice to fit an oil cooler in recirculatory oil systems. The cooling medium may be fuel or air and, in some instances, both fuel-cooled and air-cooled coolers are used.
Typical Fuel Cooled Oil Cooler. Figure 10.12. Oil system
Oil filter The pressure oil filter housing contains a wire-wound or mesh, Paper or felt elements and incorporates a by-pass valve. The filter housing can be drained independently of the main oil system. This is done through a drain valve in the housing base. When drained, the filter can be removed for examination, servicing, or replacement, as necessary, without disturbing the rest of the system. Oil system
Magnetic detectors (chip detektors) may be fitted into the oil system at various points to collect and hold ferrous debris. They are normally fitted in gearboxes and in the scavenge pump return lines to the tank. The collection of ferrous particles on the chip detector provides a warning of impending (or incipient) failure of a component. Oil system
Chip detektor - pasive type
Return oil
Chip detector
housing Premanent magnet Oil system
Oil distributing
Trent 900
Full Flow Oil System Oil system
Oil distributing
Trent 900
Full Flow Oil System Oil system
Oil distributing
Turboprop oil System Oil system
The main bearing of the engine are lubricated through oil jets. Oil system
Vent/Breather System
System of breathers (vents) will allow excess air to escape Pressure differentials between sumps, oil tank, and oil pumps keep oil flowing in correct direction Oil system
Scavenge pumps - When the oil has been distributed to all parts of the engine and has done its job, it is returned to the oil tank by either gravity or pressure from the scavenge pumps. Each pump returns the oil from a particular part of the engine and is protected by a coarse filter (or strainer) in the return line. This arrangement protects the pump gears. It also gives an indication of impending component failure if the strainers are examined for metal particles during periodical inspection Oil system
Centrifugal breather When the oil/air mixture returns to the tank the air is separated by the de-aerator tray and passes through to the gearbox via a vent line. It carries some of the oil with it in the form of a fine mist. The oil/air mist in the gearbox can then pass to the centrifugal breather. As the vanes of the centrifugal breather rotate, the oil in the mixture is caught in the vanes and thrown back into the gearbox; the air being vented to atmosphere.
Centrifugal Breather. Figure 10.17. Starting and ignition system
Starting Systems: • The starting system must ensure – rapid achievement of idling – Keep the turbine temperature in the permissible range – Repeatability of start cycle in short time , starting in flight – spinning of engine rotors without starting. • Rotor speed required for starting are in range from 10 –15% of nominal rpm • Due to the large inertia of the rotor is needed high power of starters. Starting and ignition system Starters: Used to accelerate engine to a speed at which the turbine is powering the compressor in order to allow engine operation
High pressure air (APU, GTE
Electrically driven (starter-generator
Starter/Generator Pneumatic Starter Starting and ignition system Starters:
Early systems 2 stroke engine as starter JUMO 004 engine Spouštěcí soustava Starters:
Early systems 2 stroke engine as starter JUMO 004 engine Starting and ignition system Starters:
Pneumatic Starter Starting and ignition system
* Starting and ignition system
Pneumatic Starter
Operational condition Inlet temperature Air mass flow Pressure drop Nominal output power Nominal RPM weight Starting and ignition system SAFIR 5C Starting and ignition system
Turbostarter Spouštěcí soustava
Cartrige starter Starting and ignition system Ignition Systems
• Used to ignite fuel/air in combustor • Low or high tension (voltage) systems • Intermittent or continuous duty cycle • Power supply - AC (115 vac) or DC (28 vdc)
* Starting and ignition system Ignition unit Starting and ignition system Ignition unit :
Ignition system – APU Garrett GTP-30 Starting and ignition system
Starting sequence:
Starter performance
Compressor power Turbine power consumption curve
RPM * Engine mount
* Engine mount Engine mount Engine mount Engine mount Engine monitoring
Typical monitored parameters on engine:
-Fuel Fuel pressure -Fuel Flow -Oil Quantity - Oil pressure -Oil temperature -Turbine Temperature -RPM -Vibration -Torque (turboprop/shaft) Engine monitoring
Turbine Temperature
Temperature has impact on engine performance
Exhaust Gas Temperature
Inter Turbine Temperature Engine monitoring
Vibration monitoring As engine wears, vibration levels will change, indicator of engine condition Help to predict engine life and maintenance required Engine monitoring
Power monitoring Performance Turbine Engine depends on the parameters of the ambient air. Cold air and low altitude can cause motor overload - especially turboprops
• Electronic Phase Shift
• Hydro-Mechanical GTE Variations & Applications
Thrust Producer - Turbojet
Advantages: Light, best suited for high-speed and high altitude. Gets its power from the reaction to the flow of hot gases.
Disadvantages: High fuel consumption Long take-off roll Low thrust at low forward speed GTE Variations & Applications
Thrust Producer - Turbofan Types/Categories: Low, medium, high bypass. Bypass airflow may be partially or fully ducted Long range, medium speed (Mach .99) (Hybrid compromise between the best features of the turboprop and turbojet)
Advantages: Thrust similar to turboprop Compromise of weight between turbo prop & turbo jet Not as noisy as turbo prop & turbo jet Reverse thrust possible GTE Variations & Applications
Thrust Producer - Turbofan
Bypass ratio refers to the ratio of incoming air that bypasses the core to the amount of air that passes through the engine core - Low (1-1) - Medium (2-1 or 3-1) - High (4-1 or greater) GTE Variations & Applications
Torque Producers - Turboprop/shaft Advantages: Lower fuel consumption. Short take-off (High thrust at low speed). Efficient reverse thrust.
Disadvantages: More complex design. Heavier due to the requirement for speed reduction. Normally limited to lower speed, below 500 Mph.
Turboprop: This type of engine delivers power through a shaft specifically designed to turn a propeller.
Turboshaft: This engine delivers power through a shaft, which turns a load. The load may be a pump, generator or a helicopter rotor system. GTE Variations & Applications
Torque Producers - Turboprop GTE Variations & Applications
Torque Producers - Turboshaft GTE Variations & Applications
Fixed Turbine Turbine and compressor are on same shaft GTE Variations & Applications
Free Turbine No connection between 1st and 2nd turbine (air coupling)